The present invention relates to electrode systems, devices and methods and, particularly, to electrode systems, devices and methods for use in contact with tissue (for example, skin) for electrophysical measurement.
Skin surface electrodes are important components in many medical diagnostic systems including, for example, electrocardiography (ECG), electromyography (EMG), and electroencephalography (EEG). In these systems, the electrode plays a critical role as a transducer converting physiological variables, such as those of the heart, muscles and brain, respectively, in ECG, EMG and EEG, to electrical potentials (sometime referred to as biopotentials). The measured potentials are then amplified and processed by an instrument, such as an electronic measuring circuit and a computer. The workings of skin surface electrodes are dependant on a multitude of mechanisms, such as electrode material, the electrolyte applied to the electrode, body location, and skin properties. The electrode must convert a physiological ionic current into an electronic current receivable and readable by the associated instrumentation. The electrode commonly used in clinical applications is the silver/silver chloride or Ag/AgCl electrode, which is a non-polarizable electrode that is electrochemically stable and generates relatively little noise. When using standard skin surface electrodes such as the silver/silver chloride electrode, two common preparations are typically required to lower the impedance of the electrode and of the skin contacted by the electrode: 1) an electrolyte gel containing Cl− ions is applied to maintain good ionic contact with the skin; and 2) the outmost skin layer, stratum corneum, is abraded, because it is the primary barrier to current flow due to its high ionic resistance.
Affixing surface electrodes manually is time-consuming with a high labor cost, thereby increasing medical care expenses. As the number of electrodes increases, which is desirable in, for example, certain EEG data analysis such as Laplacian mapping and source localization, manual placement of individual electrodes can become impractical, regardless of the cost. Automated placement can be desirable in such procedures. There has thus been interest in developing an automated EEG electrode placement system for use in connection with high-resolution EEG applications.
However, EEG electrodes currently used in the clinical setting exhibit a number of problems related to both manual and automatic placement. For example, such EEG electrodes have a flat contact profile with the scalp and must be delivered to the scalp without trapping hairs. In the manual placement case, various ways to handle the hair, such as combing and parting, are performed by hand. In automatic placement, however, such operations are difficult to perform. Application of electrolyte gel to a large number of electrodes through an automatic system in a reproducible manner is also difficult. In addition, the currently used gel has poor consistency and tends to spread, which could cause interference with neighboring electrodes, especially when high electrode density is required. Further, currently used gels often dry completely in approximately 1 to 2 hours, which presents a problem when long term monitoring (for example, in certain EEG procedures) is desired. Further, the depth of epidermal preparation must be carefully controlled. Otherwise, pain and infection (resulting from over preparation) or high impedance (resulting under preparation) may result. The depth of epidermal preparation is difficult to control automatically. Attempts to reduce or eliminate such problems associated with standard surface electrodes have met with limited success.
It is thus desirable to develop surface electrode systems, devices and methods that reduce or eliminate one or more of the above-identified problems as well as other problems associated with surface electrode systems currently in use.